A nightly data processing script used to run for ten minutes, and now it takes two hours. How would you find out where it's spending its time?
~4 min by voice
How to approach it
This checks whether the candidate can systematically find the cause of a performance regression: measure with profilers first, tell CPU from I/O waiting, find the algorithmic problem and connect it to data growth or code changes, rather than optimizing at random.
The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.